6.6 DataTypes

6.6.1 AnnotationDataType DataType definition

This structure contains additions as explanation and specification of the physical quantity such as "relative" for a relative velocity. The structure is defined in Table 51.

Examples are given in Table 52.

Its representation in the AddressSpace is defined in Table 53.

6.6.2 LinearConversionDataType DataType definition

This structure contains a simple conversion according to the following formula. The factors (a = inititialAddend, b = multiplicand, c = divisor, d = finalAddend) are given in a Structure. X is the source value (in source unit) and f(x) the target value (in target unit). The structure is defined in Table 54.

The values of the structure can also be used for a simple inverse conversion. It can be used if a Client wants to write a value to the Server. The value y¹ is the value that the Client wants to write to the Server in the named alternative unit and x¹ is the value the Client actually has to write to the Server instead.

Its representation in the AddressSpace is defined in Table 53.

6.6.3 ConversionLimitEnum

ConversionLimitEnum indicates whether the ServerUnit can be converted. A distinction is made between NO_CONVERSION, LIMITED and UNLIMITED. NO_CONVERSION means that no conversion is allowed (e.g. for statistical values). LIMITED conversion means that either only the conversions mentioned in the AlternativeUnits are to be used or the client requires specific know-how for the conversion. UNLIMITED means the conversion is simple and possible if the client knows the UnitSystem. The enumeration is defined in Table 56.

Its representation in the AddressSpace is defined in Table 57.

6.6.4 QuantityDimension

The QuantityDimension Structure DataType describes the dimensionality of a kind of quantity in the context of a system of units. In the SI system of units, the dimensions of a kind of quantity are expressed as a product of the basic physical dimensions length (L), mass (M), time (T), current (I), absolute temperature (θ), amount of substance (N) and luminous intensity (J) as

.

The rational powers of the dimensional exponents (α, β, γ, δ, ε, η, v), are positive, negative, or zero.

An additional dimensionless exponent is used for countable things that have no physical quantity assigned.

The QuantityDimension elements are defined in Table 58.

Its representation in the AddressSpace is defined in Table 59.

For example, the dimension of the physical quantity kind

,

the dimension of the physical quantity kind force is

,

and the dimension of the physical quantity kind “things (e.g., screws) per time” is

.

The extended SI System of units includes derived units that are built as a product of base units. That makes it difficult to compare units as SI allows an unlimited number of “SI unit strings” to describe the same quantity.

All 3 are valid SI representations of the quantity “speed” and therefore share the same quantity dimensions. A specific representation of a unit is often used to express details how the unit was measured. The dimension structure makes it much easier to identify and compare the kind of quantity of EU values.